input[type="radio"] {
    -webkit-appearance:none;
    width: 50px;
    height: 50px;
   background-color: slateblue;
}

div{
    width: 500px;
    height: 500px;
    border: solid;
    background-color: whitesmoke;
}

input:checked{
    border-radius: 10px;
}

input:checked ~ div{
    background-color: tomato;
}